Marine Invertebrates

About AquaFacts: AquaFacts are a resource for students who are looking for information on the animals at the Aquarium or other Aquarium-related topics. Here, we’ve compiled some of the most frequently asked questions that we’ve received about marine invertebrates. The answers come from our biologists and from reputable sources that we reference at the end of this page. If you have a question about marine invertebrates that’s not addressed in this page or the references below, please feel free to email our librarian.

Questions & Answers

An invertebrate is an animal without a backbone. Common examples of invertebrates include snails, clams, insects, spiders, and worms. 97 percent of all animals on Earth are invertebrates.

Are there marine invertebrates at the Vancouver Aquarium Marine Science Centre?

You can find marine invertebrates in almost every marine exhibit. The most familiar invertebrates include crabs, sea anemones, jellies, sea stars, sea urchins, sea cucumbers and shrimps. Even the octopus, one of the most popular attractions at the Aquarium, is an invertebrate.

Where do invertebrates live?

Invertebrates thrive in a wide variety of habitats worldwide. They exist on every continent, on the ground and in the air, in soil and in water. Terrestrial invertebrates such as the North African desert ant, Cataglyphis fortis, can withstand surface temperatures of more than 67°C. At the other extreme, some invertebrates exist in near-freezing waters. Some marine invertebrates, including tube worms, live on the ocean bottom near vents that expel sulphide-rich water heated to 400°C. Sulphides are poisonous to most animals, but bacteria in the tube worms’ bodies can metabolize hydrogen sulphide so it is actually a food source.

Not all invertebrates have shells. How do the rest protect themselves?

Many invertebrates have shells that protect them from both predators and losing water when they are out of water. Other invertebrates have developed defenses that allow them to survive without shells. Brightly-coloured sea slugs taste terrible to predators, sea anemones possess numerous stinging tentacles and a battery of sharp spines shield the sea urchin’s body.

Can we eat invertebrates?

Yes, you have probably eaten invertebrates without realizing it. Some common edible invertebrates are arthropods such as shrimps, prawns, crabs, crayfishes and lobsters, and molluscs such as scallops, clams, squids and octopuses. Some invertebrates that you might not have considered for your menu include snails, beetles, grasshoppers, worms and grubs.

How large can invertebrates grow?

The giant squid reaches lengths of up to 18 m; the giant clam can weigh as much as 200 kg.

Are invertebrates dangerous to people?

Many invertebrates have evolved effective defenses, making them dangerous. Scorpions, conesnails and some jellies can deliver a severe sting, while some spiders and even octopuses can bite, if harassed. Mosquitoes and certain snails may carry parasites causing diseases such as malaria, sleeping sickness, schistosomiasis and hookworm disease.

Without certain invertebrates, dead and decaying material would not break down and be recycled through the food web.

Worms and other invertebrates churn through soil that would become compacted and incapable of supporting life.

Invertebrates supply us with such ornaments as pearls and shells.

Over millions of years, the sedimented bodies of dead invertebrates have become the oil deposits that we depend on today for petroleum-fueled energy.

What do invertebrates eat?

Tiny, drifting animals, called zooplankton, live in the ocean’s surface waters and feed on tiny drifting plants, called phytoplankton. Some invertebrates are carnivorous. For example, jellies and squids often feed on fishes, while octopuses prefer crab dinners on the sea floor. Dog whelks and some sea stars prey on shellfishes, such as clams and mussels, or on barnacles. Some sea snails, chitons and limpets are herbivores that graze on algae, seaweed and other plants. Sea urchins are opportunistic omnivores. They graze on kelp or algae and scavenge the dead bodies of other animals for a meal.

How do they catch their prey?

Many carnivorous invertebrates rely on camouflage to surprise their prey. Others scavenge leftovers from the meals of other animals. Some invertebrates are parasites that live in or on other animals and derive nourishment from their host.

Some invertebrates live symbiotically with other organisms. For example, some sea anemones ride on the shells of decorator crabs; the crab provides bits of food for the sea anemone, and the sea anemone protects the crab from octopuses. Another example is the association between sea anemones and clownfish. The clownfish gain protection while the sea anemones get bits of dropped food.

How do invertebrates reproduce?

Squids, octopuses and a majority of other invertebrates reproduce sexually by copulation. Other invertebrates use the broadcast method where both male and female gametes are released into the water in enormous quantities and left to unite by chance. Many invertebrates are hermaphroditic, possessing both male and female sex organs, but they don’t usually self-fertilize. They typically look for another individual to exchange sperm with. Others reproduce asexually. Asexual reproduction results in a genetically identical copy of the parent and is characteristic of cnidarians such as corals and hydroids, some sea anemones and certain worms and sea squirts. Some invertebrate species change sex at different periods in their lives. For example, some shrimp species start life as males and later become females.

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